QTL analysis and epistasis effects dissection of fiber qualities in an elite cotton hybrid grown in second generation

The purpose of the research presented here was to explore the genetic basis of cotton (Gossypium hirsutum L.) fiber quality traits through quantitative trait locus (QTL) analysis and epistasis effects dissection, and further discuss the mechanism of heterosis. An immortalized F-2 population was developed by intercrossing Xiangzamian 2-derived recombinant inbred lines (RILs) (XZM2). Fiber quality traits were investigated in F-1 and F-2 generations of hybrid XZM2, its two parents, and the immortalized F-2 population in multiple environments in China. The low level of heterosis in XZM2 and in the immortalized F-2 population suggested a lack of dominant and dominant x dominant interaction. In general, the low correlations of genotypic heterozygosity with trait performance and mid-parent heterosis showed that heterozygosity was not always advantageous for performance, and they excluded overdominance as a major genetic basis of heterosis. A total of 50 QTLs for fiber quality were identified by single-locus QTL analysis. Although partial dominance and overdominance were detected, additive genetic variance was predominant. Common QTLs were detected both in the homozygous RlLs and in the heterozygous immortalized F-2 populations. Additionally, single-locus heterotic effects and epistasis effects at the two-locus level were detected. Our results indicated that additive gene action was the primary mechanism responsible for genetic variability in fiber quality traits. Additionally, we found that single-locus heterotic effects and epistasis effects contributed to heterosis of fiber quality traits in XZM2.